IMO classes should only get forth specs if, like druids, they already have a double role spec, or if there is a concensus that the pure dps classes should become hybrids.

For rogues specifically they don't need a forth spec right now, they need a warlock style overhaul to make the three specs feel different. When I play my rogue the only thing that really feels different for me is whether I put a dagger or slower 1h in my main hand, and which dps cooldowns I have available.

"If you have to believe it on faith, you have no reason to believe it at all.” Aron Ra

I've tanked a handful of heroic 5 mans in Cata on my Shaman before - Just took gems/chants/reforge to Agi/Dodge and Stamina. Using WF on MH and Rockbiter on OH with a Swap macro to a FT Weapon for Lavalash or Shield for expected spike damage.

Rogues that can dodge/evade tank, Shadowstepper or something. As an outsider to the class, the three specs are waaay too similar. I've been playing for years and honestly couldn't tell you the difference between Combat and Assassination, let alone all three.

I don't get the whole "hunters dual wielding pistols" thing, it's all a little too Grand Theft Auto for me. I do think Survival should be a pet-less spec, or one should/could be added. Something about a rugged loner who fends for himself and has all the tools to do so, just a cool idea to me.

Warlocks and Shaman as tanks would be cool, echoing everyone else's sentiments. If the warlock himself wasn't in some sort of demon form to take the boss' punishment himself, he could be given some sort of Dreadlord/powerful demon summon that would "tank" the boss, while the Warlock stands a short distance away and directly controls it, rather than casting spells.

Shaman, obviously, as an Earthward. The shaman calls forth the might of the earth itself!

I feel that rogues need to get a rework like warlocks did. I think 3 melee dps specs offers no variety. I would probably rework them as such

Assassination - It would be a poison based melee dps spec

Combat - The spec is described as "A swashbuckler who uses agility and guile to stand toe-to-toe with enemies." It sounds like a tanking spec so making this the evasion tanking spec would be interesting

Subtlety - Melee dps more focused on stealth

Ranger - Ok hear me out. Blizzards seems to be stubborn about giving hunters the pet-less spec. Rogues can already use rogue and use shadow magic. They could apply poison to their arrows. They seem to fight the archetype of the sly ranger than hunters do. Plus the fiasco with Shuriken Toss make me think that they would be an interesting melee/ranged hybrid.

I would try to make every class a hybird so the concept of a hybrid tax can fade away. (hopefully) For all the other classes I would give them 4th specs like:

Hunter - a tank spec. Bring back good old raptor strike. We could have them use their pet to generate aggro by transferring the aggro of the pet to the hunter like a reverse misdirect. I imagine something along the line of Rexxar and Misha.

Mage - A time base healing spec.

Warlock - Demon Hunter tank spec.

Warrior - I am having a little trouble with this one but I was thinking a Shout based spec. Not sure if it would be supportive or dps

Death Knight - Their specs are based on their runes and the only rune left is Death. This spec would be the Necromancer archetype. I would love to see a death knight summon some caster skeletons.

Monk - A chi/wind based ranged dps spec

Priest - A tank spec on a priest would feel too much like a paladin. I feel the priest 4th spec would be another dps spec that either involves more psychic themes or perphaps a balance of shadow and holy.

Paladin - Holy shock/ denounce ranged dps spec. possibly convert str to spell power instead of attack power. Maybe have an ability that increases the range of auto attacks and Crusader strike. For anyone who play league of legends I was thinking of something like Kayle.